1. Field of the Invention
The present invention relates to a method for spreading thin soft rectangular articles such as bed sheets, diapers, table cloths, handkerchieves, cloth wrappers, dress materials, all other cloths, unwoven cloths, paper sheets, plastic sheets or the like (hereinafter generally called "rectangular sheets" throughout the specification and claims), and more particularly to a method for gripping corners of rectangular sheets that is available in a spreading apparatus for rectangular sheets, a sorting apparatus for linens or other textile goods, a spreading apparatus for linens or the like before laundry, and the like.
2. Description of the Prior Art
Generally, in a laundry factory, arriving bed sheets, towels, cover cloths and the like (hereinafter called "sheets") are washed as by a continuous washing machine, and thereafter they are charged into a drying machine through a dewatering step, as shown in FIG. 16. Then, sheets having passed through a drying step are untangled and spreaded out, and after they have been subjected to ironing, they are folded and shipped. At this time, between the drying step and the ironing step, sheets taken out of a drying machine are conveyed to a predetermined location by means of a belt conveyor, these sheets are picked and spreaded one by one from a block of sheets piled in heaps by a several workers, and then they are fed to an ironing apparatus or its auxiliary apparatus (spreader, feeder or the like).
A spreading work for sheets having finished a drying step is heavily laborious for workers under an unfavorable environment because it is a work within a high-temperature high-humidity atmosphere. Therefore, heretofore development of an apparatus for automating a spreading work for sheets has been desired, but such an automated apparatus does not exist in the industry at present, and as a prior art, only a fixed-position holding method for sheets was proposed in Japanese Patent Publication No. 59-24685 (1984).
This method consists of a first step of suspending a sheet while holding a part thereof, a second step of holding the lowermost end of the sheet suspended in the aforementioned first step and suspending the sheet while releasing the holding in the first step, a third step of holding the lowermost end of the sheet suspended in the second step, and a fourth step of gripping the sheet at the two points held in the above-mentioned second and third steps as stretched horizontally, and with respect to a rectangular sheet the method will be explained in more detail in the following.
If a rectangular sheet S is suspended while holding any arbitrary one point 027 thereon as shown in FIG. 17 in the first step, then a straight line passing through the held point 027 and a center of gravity 028 of the sheet S becomes vertical. Next, in the second step the sheet S is suspended while holding the lowermost point 029 under this condition and the holding in the first step is released. As the third step, then the sheet S takes the attitude shown in FIG. 18, and the distance between the top end 029 being held and the bottom end 030 of the sheet S becomes constant. Hence in the third step, the bottom end 030 shown in FIG. 18 is held. Next, in the fourth step if the top end 029 and the bottom end 030 which are the held points in the second and third steps, respectively, are held horizontally, the sheet S takes the state shown in FIG. 19. Under this condition one may consider that the sheet S has been held at fixed positions, and it could be transferred to the next process. However, in order to hold the sheet S under an undoubled spreaded condition, in a fifth step one of the bottom ends 031 and 032 in FIG. 19 is held and one of the previously held points 029 and 030 is released.
FIG. 20 is a schematic front view of a sheet fixed-position holding apparatus that is available upon practicing the above-described method for holding a sheet at fixed positions, and for convenience of explanation the subject apparatus is severed into four sections A, B, C and D. The construction of this sheet fixed-position holding apparatus is such that initial holding of a sheet and detection and holding of one corner of the sheet are carried out in the section A, detection and holding of another corner diagonally opposite to the corner held in the section A are carried out in the section B, in the sections B and C the sheet having its diagonally opposite two corners held is suspended with the diagonal kept horizontal and further holding of only one of the corners at the bottoms of the doubled sheet portion is carried out, and in the sections C and D adjacent two corners at the opposite ends of one edge of the sheet are held at the same level, and thereby the sheet S can be spreaded and held at fixed positions. In these figures, a stroking rod 035 is provided in the proximity of a terminal end of rightward movement of a chuck 033 so as to be movable vertically along a guide slot 036.
A chuck 037 is provided so as to be movable vertically along a guide slot 038 at a location under the terminal end of rightward movement of the chuck 033 and also to be movable from a lower dead point obliquely in the right-upward direction along the same guide slot 038. Another stroking rod 039 is provided so as to be movable vertically along a guide slot 040 in the proximity of an upper dead point of the oblique movement of the chuck 037. A chuck 041 is provided so as to be movable obliquely along a guide slot 042 with its lower dead point located under an upper dead point of the oblique movement of the chuck 037. A chuck 043 is provided so as to be movable vertically along a guide slot 044 at a location under a middle point of the line connecting the upper dead points of the respective oblique movements of the chucks, 037 and 041, and also so as to be movable obliquely along the same guide slot 044 with the uppermost point of the vertical movement placed at the lowermost point of the oblique movement. It is to be noted that the chucks 033, 037, 041 and 043 and the stroking rods 035 and 039 are driven along the respective guide slots by air cylinders not shown.
In order to hold a rectangular sheet at fixed positions by means of the above-described sheet fixed-position holding apparatus, the operation is carried out in the following sequence.
At first, in the state shown in FIG. 21, a part of a sheet 045 to be held at fixed positions is detected and held by the chuck 033, and this chuck 033 rises along a guide slot 034 then moves rightwards and becomes the state shown in FIG. 22. In the state shown in FIG. 22, as the lowermost end of the sheet 045 suspended by the chuck 033 would not always come right above the chuck 037, the sheet 045 is stroked by a stroking rod 035 including a circular ring having a notch at one portion so that the lowermost end of the sheet 045 (a corner portion of the sheet 045) may come right above the chuck 037 which is positioned right under the chuck 033. Thereby, when the chuck 037 rises, it can hold one of the corners of the rectangular sheet 045 at the lowermost end of the sheet as shown in FIG. 23. Thereafter the chuck 033 releases the sheet 045. Also, the chuck 037 lowers and then rises in the right upper direction along the guide slot 038. It is to be noted that at this moment the stroking rod 035 returns to an upper dead point of a guide slot 036.
In the state shown in FIG. 24, the sheet 045 suspended by the chuck 037 which has come to the upper dead point of the guide slot 038 and directed downwards, is again stroked by a stroking rod 039, and since the lowermost end (the corner diagonally opposite to the corner held by the chuck 037) of the sheet 045 comes to the position of a chuck 041 (a fixed position determined depending upon the size of the sheet 045), the end is detected and held by the chuck 041. The chuck 041 holding the lowermost end of the sheet 045 rises up to an upper dead point along a guide slot 042, and so, as shown in FIG. 25 two diagonally opposed corners of the sheet 045 are held at the same level (that is, horizontally). It is to be noted that at this moment the stroking rod 039 returns to an upper dead point of a guide slot 040.
Next, in the state shown in FIG. 25, the sheet 045 having its one diagonal held horizontally with the corners at the opposite ends of the diagonal gripped by the chucks 037 and 041, has one of two hanging corners gripped by a chuck 043 disposed at that position as opposed to the chuck 041, while the chuck 037 is released, and by raising the chuck 043 along a guide slot 044, the sheet 045 can be held at fixed positions in a vertically elongated attitude. It is to be noted that in this sheet fixed position holding apparatus, since the distance between the upper right end position of the chuck 037 and the lower left end position of the chuck 041 is adjusted to be nearly equal to the length of the diagonal of the sheet to be treated, in the event that the chuck 037 should have gripped two adjacent corners of the sheet 045 together in the state shown in FIG. 23, the chuck 041 could not grip the sheet 045, and so it is compelled to again repeat the above-described holding operation for the sheet 045.
However, the sheet gripping mechanism used in the sheet fixed-position holding apparatus in the prior art involved the following problems, That is, since the chucks 037, 041 and 043 are respectively disposed at fixed positions, the apparatus could spread only a rectangular sheet of predetermined sizes, and it was practically not useful for sheets in which various sizes of sheets were mixed.
In addition, as shown in FIG. 25, in order to made the chuck 043 grip one corner of the sheet 045 while being spreaded from the section B to the section C, it was essentially necessary to grip the sheet 045 with its diagonal stretched horizontally, and so, the entire apparatus necessitated a broad space. Furthermore, as the chucks 037 and 041 grip the lowermost ends of the sheet 045 always after the sheet was made to hang down in the direction of the gravity, at the gripped portions of the sheet, folds, creases, twists or the like would be necessarily generated, and in some cases they would adversely influenced upon finishment by the subsequent ironing apparatus or the like.